Distribution of keratin subtypes in the thymus of Japanese black calves during acute thymic involution.

Immunohistochemistry for keratins 5, 8, 14, and 18 was performed on Japanese Black calf thymuses at various stages of acute thymic involution. Keratins 5 and 14 were predominantly localized in the thymic medulla, while keratins 8 and 18 were broadly distributed throughout the parenchyma. Despite thymic involution, the distribution patterns of these keratins remained consistent. The cortical area, assessed by keratin 5 staining, progressively decreased with involution but retained approximately 40% of the total parenchyma even at the most severe stage. These results suggest that the thymic cortex shrinks but does not completely disappear during acute thymic involution in calves.